This invention relates to a femoral prosthesis of the type which employs a short stem. The term short stem is used herein to indicate a stem which only extends into the femur up to or slightly beyond the neck beneath the head. Short stems of this type are being developed by the Applicant to preserve bone stock for young patients.
Numerous short stem designs have been developed and used on the market over the last 50 years. Clinical results and finite element analysis have shown that most of these stems, which were designed to preserve bone stock, are in fact leading to bone resorption in proximal areas of the femur and bone formation in the distal contact area of the stem with the femur.
WO 86/03962 shows a stem of this type has been used by surgeons. Unfortunately the first generation of instrumentation was unprecise and the clinical results were poor when the stem was malpositioned on the femur (too much varus, lack of contact on proximal/medial cortex). On the other hand when the stem was well positioned the clinical results were successful and still are after 18 years clinical follow-up. It has been confirmed that the stem design keeps most of the natural stress distribution in the femur when well positioned but the problem is preventing malpositioning.